Antarctic Krill ( Euphausia superba ) swimming behaviour changes within a vertical flume under varied light, flow and chemical conditions

Reacting strongly to light, chemicals or other aspects of their environment is common in zooplankton species. This study investigated if up- and down-welling currents operate with forces and speeds high enough to be felt and therefore have an impact on the behaviour of a macrozooplankton (the Antarctic krill, Euphausia superba ). Agent-based models incorporating extremely simple behavioural responses have provided insight into some aspects of krill distributions, particularly diel vertical migration. More detailed and accurate predictions through modelling are only possible with well-resolved relationships between environmental properties (light, flow, food abundance, predator cues) and observed behaviours. This study attempted to unravel some of these complex relationships between the environment and krill behaviour by investigating the swimming responses of E. superba in a vertical flume to up- and down-welling, the presence of phytoplankton and predator cues and different photic inputs. This study found that even very slow flows in up-and down-welling polarise krill movement changed and that the sensitivity of krill to up- and down-welling is modified by the presence of food and predator cues. Thus, it is possible to quantify krill behavioural responses to environmental stimuli in a way that permits more detailed agent-based models capable of examining krill responses to cues in nature. These results complement previous studies on krill behaviour and add an extra dimension to modelling work of krill swimming dynamics, distributions and demographics under a range of environments.